Aggression within the family is pervasive and has considerable adverse effects on children. Given surprisingly high rates of inter-parental aggression among couples with young children and the increased likelihood of parent-to-child aggression among aggressive couples, this study is designed to examine the co- occurrence of inter-parental and parent-to-child aggression. The primary aim of the project is to determine the relative frequency and direction of within-incident aggression spillover (i.e., the direct transfer of aggression from one family subsystem to another family subsystem). Such information will assist in understanding whether the adverse outcomes for children who witness inter-parental aggression may be partly due to children being the targets of aggression within the same immediate context of inter-parental aggression. In addition, it will help determine whether the co-occurrence of family aggression is due to one form of aggression either directly or indirectly leading to another form of aggression, as well as shared etiological factors. To better understand the process and context of aggression spillover, relations between within-incident aggression spillover and incident-specific predictor variables will be examined. Further, to identify which families are at risk for experiencing aggression spillover, relations between longitudinal individual- and family-level variables and aggression spillover will be examined. This work will indicate whether constructs assessed as traits or behavioral tendencies function at the level of the incident to predict aggression and aggression spillover. This project will leverage recruitment and data collection efforts from an existing community sample of 125 couples. When their first-born child is three years old, measurement of the processes and context of family aggression will be added through in-depth quarterly telephone interviews with each parent. Non-identifiable data collection techniques will be used to minimize under-reporting. This sample is perfectly designed for the success of the study aims as it includes high- and low-risk families, and early childhood is a time of increased family stress when rates of PCA begin to peak and children are most likely to be involved in episodes of IPA. This study will offer a better understanding of the context, processes, and mechanisms of aggression spillover, providing a means with which to interpret the substantial inter-parental and parent-to-child aggression co- occurrence rates. In turn, more valuable theories regarding the processes and family dynamics involved in family aggression will be developed. The methodology will provide a means of assessing family aggression that gets closer to the incident than prior studies, while maintaining feasibility and alleviating many limitations of often used measures family aggression. By examining the function of predictor variables at the level of the incident, greater causal inference will be gained. Further, this work will provide a conceptual, empirical, and methodological integration of the traditionally distinct fields of marital and parent-child aggression. Study results will foster the development of effective prevention and treatment models that address the intertwined nature of family conflict. PUBLIC HEALTH RELEVANCE: Exposure to inter-parental aggression and the experience of parent-to-child aggression frequently result in substantial adverse psychological and physical outcomes for children. To understand, and ultimately intervene in, the perpetration of family aggression, we must know whether one form of family aggression directly leads to the other form of family aggression within the same incident of aggression. Knowing the frequency with which such "spillover" occurs, as well as the contextual and longitudinal variables that predict spillover, will help us to refine existing prevention and intervention programs, resulting in substantial public health benefits for couples and their children.